For the reasons above, I think it would be worth it. And I imagine that the 6000 lines are pretty short. But would there be a way to check with the XenForo peeps that nobody is working on these translations already, just in case? It would be a pity to do that work if they say that they almost have it ready, done by someone else.I would also take the translation files and offer them for free with no strings attached on the XenForo Resources site, with a donate button. Most likely, no one will donate anything. But it would get us "out there" as the nice people on Cassiopaea who did what no one else would do. People are looking for Spanish especially, and French...
Then more people would use XenForo, we'd get "credit" for being awesome, and XenForo would spread. Which means it would get better.